Aqueous cleaning compositions exhibit a tendency toward foaming because they contain surface active agents such as soaps, and synthetic detergents. In many instances, such cleaning compositions produce excessive foam and the user must use substances known as anti-foaming agents or defoamers. Some defoamers such as silicones tend to interfere with the function of the cleaning compositions in that unwanted residues are left after the cleaners are wiped off while others are environmentally unacceptable because they are not biodegradable.
Alkyl polyglycosides are a class of nonionic surfactants that exhibit significantly higher foaming profiles than other nonionic surfactants, such as alcohol ethoxylates. In fact, it can be said that the foaming tendencies of alkyl polyglycosides more closely resemble those of anionic surfactants, such as alcohol sulfates, than the foaming tendencies of other nonionic surfactants. This higher foaming tendency makes the use of alkyl polyglycosides undesirable for many applications, e.g., cleaning-in-place for food processing plants, high pressure spray cleaning, bottle washing, floor cleaners and automatic dishwashing, wherein high levels of foam interfere with the cleaning and rinsing operation and reduce the efficiency of the operation.
Low foam nonionics, such as EO/PO block copolymers, can be used to reduce the foaming properties of alkyl polyglycoside surfactants, but these materials have undesirable properties, e.g., low biodegradability, relatively high aquatic toxicity and poor caustic compatibility.
Accordingly, there is a need for the development of defoamers that do not interfere with the cleaning ability of aqueous cleaning compositions and that are biodegradable, exhibit low aquatic toxicity and good caustic compatibility.
Certain alkyl polyglycosides, most notably C.sub.12-16 alkyl polyglycosides, have a tendency to crystallize during storage at ambient temperatures due to their supersaturated state. These same alkyl polyglycosides also exhibit unacceptably high viscosities which makes transferring them such as by pouring or pumping difficult. Upon crystallization, the alkyl polyglycosides become turbid, i.e., cloudy and opaque in appearance due to the solids contained therein falling out of their supersaturated state which, when coupled with the resultant non-homogeneous state of the crystallized solution and the attendant difficulties in handling operations such as pumping, is a highly undesirable phenomenon. In order to rectify this undesirable physical state, the alkyl polyglycoside composition must be heated in order to resolvate the crystals. As can be imagined, this process is both expensive and time-consuming. Thus, there is a need for methods of either reducing or eliminating the tendency of alkyl polyglycosides to crystallize during prolonged storage under ambient conditions. There is also a need for viscosity reducing additives which are more efficient than current additives since conventional additives must be added in amounts of up to 8% by weight to achieve certain desired viscosity reductions.